Composite bump bonding

ABSTRACT

A bonded structure comprising the physical and electrical connections between an integrated circuit element and substrate using a composite bump comprised of a single polymer body of low Young&#39;s Modulus and a conductive metal coating. When the bonded structure is formed the composite bump is deformed and the low Young&#39;s Modulus of the polymer body allows a very reliable bonded structure with very low bonding force. Due to the low Young&#39;s Modulus there is little tendency to separate the connections after the bonded structure is formed. The bond can be formed using thermocompression bonding, ultrasonic bonding, application of heat or application of light. The bond can also be formed using a non conductive adhesive between the integrated circuit element and the substrate. The bond can also be formed with a conductive adhesive coating on the composite bump.

RELATED PATENT APPLICATIONS

[0001] (1) (E83-0003), Ser. No. ______, filed ______, entitled CompositeBump Structure and Methods of Fabrication assigned to the same assignee.

[0002] (2) (E83-0004), Ser. No. ______, filed ______, entitled CompositeBump Flip Chip Bonding assigned to the same assignee.

BACKGROUND OF THE INVENTION

[0003] (1) Field of the Invention

[0004] The invention relates to the joining of integrated circuitelements to the next level of integration, or that level of integrationto the following level, and more particularly to the formation of thebonded structure which comprises the physical and electrical connectionbetween the integrated circuit element and the next level ofintegration.

[0005] (2) Description of the Related Art

[0006] In the manufacture of highly dense integrated circuits theformation of an inexpensive and highly reliable mechanical bond andelectrical interconnection between the integrated circuit element andsubstrate has long been recognized to be of key importance. Some timeago a solution to this need was patented by L. F. Miller et al in U.S.Pat. No. 3,401,126. This method worked well for many years butincreasing levels of integration and circuit density have made the needfor interconnections on an increasingly fine pitch of key importance.

[0007] A method for achieving increased interconnection density waspatented by K. Hatada in U.S. Pat. No. 4,749,120. This method employs ametal bump as the electrical interconnection between the integratedcircuit chip and the substrate while holding the integrated circuit chipin place with a resin coating on the substrate acting as an adhesivebetween chip and substrate. This method has the disadvantage of arelatively high Young's Modulus for metals. As a result of the highYoung's Modulus a very large bonding force is required between theintegrated circuit chip and the substrate during the micro-bump bondingprocess while the resin is undergoing its curing cycle. After thebonding process the gold micro-bump will tend to return to its originalshape and the recoil forces will disengage some of the micro-bumps fromthe electrodes on the substrate. Another method patented by Y. Tagusa etal in U.S. Pat. No. 4,963,002 employs nickel plated plastic beads orsilver particles to achieve the electrical connection, but the formersuffers from small contact surface area and the latter suffers thedisadvantage of a relatively high Young's Modulus for silver.

[0008] U.S. Pat. No. 4,916,523 issued to Sokolovsky et al shows aunidirectional conductive adhesive to bond the integrated circuit chipto the substrate. U.S. Pat. No. 5,134,460 issued to Brady et al showsconductive metal bumps coated with a gold layer.

SUMMARY OF THE INVENTION

[0009] It is the principal object of the invention to provide a bondedstructure comprising the electrical and physical connections betweenintegrated circuit elements and the corresponding substrate wherein verydense wiring patterns can be accommodated economically and the resultingconnections are extremely reliable.

[0010] This object is achieved with a bonded structure comprising theintegrated circuit element input/output pads, composite bumps comprisedof a single polymer body with a Young's Modulus which is low compared tometals and a conductive metal coating covering the polymer body, and thesubstrate input/output pads. The conductive metal coating covering thepolymer body must be chosen to provide good adhesion to the polymer bodyand may include an adhesive layer and a barrier layer in addition to aconductor layer. The low Young's Modulus of the polymer, about 0.4×10⁶to 0.5×10⁶ psi, allows the bond to be made with very low bonding forceand greatly reduces or eliminates the force tending to separate theconnections after the bonding force is removed. This results inextremely reliable physical and electrical connections between theintegrated circuit element and substrate.

[0011] It is a further object of the invention to provide a method offorming a bonded structure comprising the electrical and physicalconnections between integrated circuit elements and the correspondingsubstrate wherein very dense wiring patterns can be accommodatedeconomically and the resulting connections are extremely reliable.

[0012] This object is achieved by forming a bonded structure comprisingthe integrated circuit element input/output pads, composite bumpscomprised of a single polymer body with a Young's Modulus which is lowcompared to metals and a conductive metal coating covering the polymerbody, and the substrate input/output pads. The conductive metal coatingcovering the polymer body must be chosen to provide good adhesion to thepolymer body and may include an adhesive layer and a barrier layer inaddition to a conductor layer. The composite bump will be deformedduring the bonding process and the low Young's Modulus of the polymer,about 0.4×10⁶ to 0.5×10⁶ psi, allows the bond to be made with very lowbonding force and greatly reduces or eliminates the force tending toseparate the connections after the bonding force is removed. The polymerbody and the conductive metal coating must be chosen to be compatiblewith the temperatures used during the bonding process.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a cross sectional representation of the composite bumpformed on the integrated circuit element showing the polymer interiorand conductive metal coating of the composite bump.

[0014]FIG. 2 is a cross sectional representation of the bonded structurewith the composite bumps formed on the integrated circuit element priorto bonding.

[0015]FIG. 3 is a cross sectional representation of the composite bumpformed on the substrate showing the polymer interior and conductivemetal coating of the composite bump.

[0016]FIG. 4 is a cross sectional representation of the bonded structurewith the composite bumps formed on the substrate prior to bonding.

[0017]FIG. 5 is a cross sectional representation of the composite bumpformed on both the integrated circuit element and the substrate showingthe polymer interior and conductive metal coating of the compositebumps.

[0018]FIG. 6 is a cross sectional representation of the bonded structurewith the composite bumps are formed on both the integrated circuitelement and the substrate prior to bonding.

[0019]FIG. 7 is a cross sectional representation of the bonded structurewherein a conducting adhesive bonds the conducting metal coating of thecomposite bump to the substrate input/output pad.

[0020]FIG. 8 is a cross sectional representation of the bonded structurewherein a conducting adhesive bonds the conducting metal coating of thecomposite bump to the integrated circuit element input/output pad.

[0021]FIG. 9 is a cross sectional representation of the bonded structurewherein a conducting adhesive bonds the conducting metal coating of theintegrated circuit element composite bump to the substrate compositebump.

[0022]FIG. 10 is a cross sectional representation of the bondedstructure wherein a non conducting adhesive bonds the integrated circuitelement to the substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Refer now more particularly to FIGS. 1 and 2, there is shown anembodiment for the bonded structure of the current invention. Compositebumps are formed on the integrated circuit element 30 input/output pads26. The input/output pads are formed of a metal such as aluminum with adiameter of about 90 microns. Each composite bump comprises a singlepolymer body 32 and a conductive metal coating 36 covering the polymerbody. The polymer body must withstand temperatures encountered duringbonding and can be polyamic acid polyimide such as PROBIMIDE 7010 orPROBIMIDE 514 produced by OCG Microelectronic Materials, Inc., Tempe,Ariz. The polymer body has a thickness of between about 5 and 25microns. Input/output pads 24 are formed on the substrate 20 using ametal such as aluminum.

[0024] The conductive metal coating 36 must adhere to the polymer bodyand can be a metal such as aluminum or nickel; or a composite such asnickel/gold, chrome/gold, chrome/silver, or titanium/platinum. Theconductive metal coating can be a composite which includes an adhesionlayer/a barrier layer/a conductor layer such as chrome/copper/gold,chrome/nickel/gold, chrome/silver/gold, titanium/platinum/gold,titanium/palladium/gold, or titanium/tungsten/silver.

[0025] When the bonded structure is formed the composite bumps willcontact the substrate input/output pads and will be deformed as shown inFIG. 2 so that each composite bump will contact a substrate input/outputpad. Due to the low Young's Modulus of the polymer body a very smallforce, about one tenth that required by the traditional gold bump, isrequired for this deformation and there is little tendency to separatethe bonded structure after it has been formed.

[0026] Refer now to FIGS. 3 and 4, there is shown another embodiment ofthe bonded structure. In this embodiment the composite bumps are formedon the substrate input/output pads 24. The composite bump and thestructure after the bond is formed is as described above.

[0027] Another embodiment is shown in FIGS. 5 and 6. in this embodimentthe composite bumps are formed on both the integrated circuit elementinput/output pads 26 and the substrate input/output pads 24. When thebonded structure is formed the substrate composite bumps are broughttogether with the integrated circuit element composite bumps. Thecomposite bumps are deformed and due to the low Young's Modulus of thepolymer body a very small force is required for this deformation andthere is little tendency to separate the bonded structure after it hasbeen formed.

[0028] The integrated circuit element 30 and the substrate 20 arebrought together so that the conductive metal coating 36 on eachcomposite bump contacts a substrate input/output pad 24 as shown in FIG.2, an integrated circuit element input/output pad 26 as shown in FIG. 4or a corresponding composite bump as shown in FIG. 6. The bond is thenformed using a bonding process such as thermocompression bonding,ultrasonic bonding, tape automated bonding, application of heat energy,or application of light energy.

[0029] As shown in FIGS. 7, 8, and 9 the bonding may also beaccomplished using a conductive adhesive 38 between the conductive metalcoating 36 of each composite bump and the corresponding substrate pad 24shown in FIG. 7, the corresponding integrated circuit elementinput/output pad 26 shown in FIG. 8, or the corresponding composite bumpshown in FIG. 9. As shown in FIG. 10, the bonding may also beaccomplished using a nonconductive adhesive 22 between the integratedcircuit element 30 and substrate 20. The conductive and nonconductiveadhesives may require the application of heat energy or light energy.During the bonding process the polymer body in each composite bump isdeformed as electrical connection is formed. This deformation isimportant in forming a good electrical contact. Due to the low Young'sModulus of the polymer body this deformation requires a very smallbonding force and produces little or no tendency to separate theconnection after it has been made.

[0030] While the invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A bonded structure, comprising: an integratedcircuit element having input/output pads; a substrate havinginput/output pads; and a plurality of physical and electricalconnections between said integrated circuit element input/output padsand said substrate input/output pads wherein each said connectionincludes a composite bump comprised of a polymer body and a conductivemetal coating covering said polymer body, and wherein said compositebump is deformed when said connection is formed.
 2. The bonded structureof claim 1 wherein said polymer is polyamic acid polyimide.
 3. Thebonded structure of claim 1 wherein said conductive metal coating iscomprised of an adhesion layer, a barrier layer and a conductor layer.4. The bonded structure of claim 1 wherein said composite bumps areformed on said integrated circuit element input/output pads prior toformation of said connection.
 5. The bonded structure of claim 1 whereinsaid composite bumps are formed on said substrate input/output padsprior to formation of said connection.
 6. The bonded structure of claim1 wherein said composite bumps are formed on both said integratedcircuit element input/output pads and substrate input/output pads priorto formation of said connection.
 7. A method of forming a bondedstructure, comprising: providing an integrated circuit element withinput/output pads; providing a substrate with input/output pads;providing composite bumps comprised of a polymer body and a conductivemetal coating covering said polymer body formed on said integratedcircuit input/output pads; bringing together said integrated circuitelement and said substrate so that said composite bumps contact saidsubstrate input/output pads and are deformed during said contact; andbonding said composite bumps to said substrate input/output pads.
 8. Amethod of forming a bonded structure, comprising: providing anintegrated circuit element with input/output pads; providing a substratewith input/output pads; providing composite bumps comprised of a polymerbody and a conductive metal coating covering said polymer body formed onsaid substrate input/output pads; bringing together said integratedcircuit element and said substrate so that said composite bumps contactsaid integrated circuit element input/output pads and are deformedduring said contact; and bonding said composite bumps to said integratedcircuit element input/output pads.
 9. A method of forming a bondedstructure, comprising: providing an integrated circuit element withinput/output pads; providing a substrate with input/output pads;providing composite bumps comprised of a polymer body and a conductivemetal coating covering said polymer body formed on said integratedcircuit input/output pads and on said substrate input/output pads;bringing together said integrated circuit element and said substrate sothat said integrated circuit element composite bumps contact saidsubstrate composite bumps and said integrated circuit element compositebumps and said substrate composite bumps are deformed during saidcontact; and bonding said integrated circuit element composite bumps tosaid substrate composite bumps.
 10. The method of claim 7 wherein saidpolymer is polyamic acid polyimide.
 11. The method of claim 7 whereinsaid conductive metal coating is comprised of an adhesion layer, abarrier layer and a conductor layer.
 12. The method of claim 7 whereinsaid bonding is provided by a conductive adhesive between said compositebumps and said substrate input/output pads.
 13. The method of claim 8wherein said bonding is provided by a conductive adhesive between saidcomposite bumps and said integrated circuit input/output pads.
 14. Themethod of claim 9 wherein said bonding is provided by a conductiveadhesive between said substrate composite bumps and said integratedcircuit composite bumps.
 15. The method of claim 7 wherein said bondingis provided by a nonconductive adhesive between said integrated circuitelement and said substrate.
 16. The method of claim 7 wherein saidbonding is provided by thermocompression bonding.
 17. The method ofclaim 7 wherein said bonding is provided by application of heat energy.18. The method of claim 7 wherein said bonding is provided byapplication of light energy.
 19. The method of claim 7 wherein saidbonding is provided by ultrasonic bonding.
 20. The method of claim 7wherein said bonding is provided by tape automated bonding.